Lewis & Short

ĭn-artĭfĭcĭālis, e, adj., inartificial, not according to the rules of art (post-Aug.): illas (probationes) ἀτέχνους, id est inartificiales; has ἐντέχνους, id est artificiales vocaverunt, Quint. 5, 1, 1: probationes, id. 5, 5, 2; cf. id. 5, 10, 11: argumenta, Mart. Cap. 5, § 474; § 557; § 560.
Adv.: ĭnartĭfĭ-cĭālĭter, inartificially: se gerere (opp. artificialiter), Quint. 2, 17, 42.